I entered in my GMail account and the webapp prompted in Firefox. I accepted and now, I want to change the GMail webapp account, but there is no option and, inside the "online accounts" from system config, there is no GMail configuration. Could you tell me how to change account or delete them?
See if Ubuntu Web Apps is listed here: https://profiles.google.com/connectedaccounts If it is, remove it.
Run the command:
Find 'allowed domains' in
Remove mail.google.com from the entry.
Visit gmail again, using the new account this time, and it'll ask you again to enable it.